1. Field of the Invention
The present invention is directed to a retention system for a piston in an actuated fastener driving tool.
2. Description of the Related Art
Actuated fastener driving tools are used in many applications, such as driving fastening pins into concrete or steel. It is common for a driving tool to have a driving means such as explosive powder, combustion of gasoline, or compressed air which acts upon a piston which travels in a barrel. U.S. Pat. No. 5,273,198 assigned to Illinois Tool Works Inc. discloses a powder-actuated fastener driving tool for driving fasteners, such as drive pins, into concrete, masonry, or steel substrates.
It is desirable for actuated fastener driving tools to have a mechanism for retaining a piston in the barrel in a rearward position prior to firing of the tool to maintain the optimum chamber volume for optimal performance of the tool. U.S. Pat. No. 4,941,391 discloses the use of ball bearings at the muzzle of the tool for retaining the piston in the most rearward position with a set of springs providing the force to urge the bearings toward the piston. U.S. Pat. Nos. 5,950,900 and 6,092,710 also disclose the use of bearings to retain the piston, but instead use a spring washer and a ring, respectively, to provide the force upon the bearings to urge them towards the piston.
While the retention devices of U.S. Pat. Nos. 4,941,391, 5,950,900 and 6,092,710 may be effective in retaining the piston during normal operation, they present problems due to their complexity and their positioning within the tool. The springs, spring washers, rings and bearings of the prior retention components are all items that wear down due to the large, violent, and frequent forces exerted by the piston. The components are generally placed within the muzzle of the tool and the entire muzzle must be disassembled to replace the wear items. Also, because the retention components themselves are complex, they require excessive disassembly and reassembly time for the retention components to function properly.
U.S. Pat. Nos. 4,941,391, 5,273,198 and 5,950,900 also disclose a buffer for absorbing shock from the piston. The buffer provides a method for dampening the piston when it is driven to avoid damage to the piston or the tool. The buffer is also a wear item that is usually placed in the barrel of the tool to absorb shock before it can be felt in the muzzle or other parts of the tool.
What is needed is a piston retention system that eliminates the need of a complicated design with springs, washers or rings within the fastener driving tool. Also what is needed is a system that allows the easy and simultaneous change-out of both of the wear items, the bearings and the buffer, to allow shortened maintenance times for the tool.
It is an object of the present invention to provide a simplified piston retention system for a fastener driving tool to retain a piston in a predetermined position when the tool is not being fired.
It is another object of the invention to provide a piston retention system that incorporates a set of bearings and the buffer so that the bearings may be removed from the muzzle and so that the wear items of the bearings and the buffer may be placed in the same general location for easy maintenance change-out.
In accordance with the present invention a piston retention system is provided for a fastener driving tool. The piston retention system for an actuable piston includes a buffer for absorbing shock from the piston, a set of bearings abutted against the buffer and a cage for retaining the bearings. The buffer is situated so that it provides a force upon the bearings, urging the bearings radially inward towards the piston so that the piston is retained in a predetermined position when the piston is not being actuated. The actuable piston, the buffer, the bearings and the cage are placed within a barrel of a piston guide of a fastener driving tool. A muzzle having a through bore may also be connected to the piston guide to guide the piston as it is being driven and to guide a fastener being driven by the piston.
The present invention simplifies the design of the piston retention system by combining the buffer with the bearings and eliminates the need for a complicated apparatus in the muzzle. The simplified design also provides for less expensive manufacturing costs.
The novel piston retention system of the present invention allows for the rapid and easy modular change-out of both the bearings and the buffer, both of which are wear items. This modular change-out improves maintenance time and costs.
These and other objects, features and advantages are evident from the following description of an embodiment of the present invention, with reference to the accompanying drawings.